Magnetic separation device, adapted for magnetic particle purification and/or separation, can effectively separate a trace amount of an entity of interest from a compound or mixture for obtaining such entity with high purity. However, in a conventional magnetic separation process, usually a number of washing cycles are carried out after magnetic particles are separated and the unwanted liquid phases are removed, each including repetitive elution and aspiration processes. Owing to the performing of such washing cycles usually requires the test tubes to be taken out of the magnetic separation device, splashing of the contents will occur, possibly causing cross-contamination between test tubes or contamination of an operator, not to mention that it is time-consuming and inconvenient when there are a plenty of test tubes required to be taken out.
There are two types of magnetic separation device. One of which is shaped like a rod, a pen or a pipette such as those disclosed in U.S. Pat. No. 6,468,810, entitled “Magnetic particle transfer device and method”, U.S. Pat. No. 5,647,994, entitled “Method and apparatus for separating magnetic particles from a solution”, and U.S. Pat. No. 6,455,325, entitled “Liquid processing method making use of pipette device and apparatus for same”. The aforesaid devices usually immerse a magnetic probe directly into a solution for attracting magnetic particles along with targeted bio-substances attached thereupon. Nevertheless, they are disadvantageous in that: the magnetic portion of the probe must be covered by disposable protective membrane, that although cross-contamination between solutions of different test tubes can be prevented, it is troublesome to operate. Moreover, as the separation of magnetic particle in such devices require the probe to contact with the solution directly, the purification efficiency can easily be adversely affected when the probe is contaminated and adhered by some nonspecific impurities which also might cause some damage to the intended targeted bio-substances.
Another type of magnetic separation device uses magnetic members to apply magnetic forces on solution-containing test tubes from the outside thereof, such as a non-contact magnetic separation device disclosed in U.S. Pat. No. 5,705,062, entitled “Analytical device for separating magnetic micro-particles from suspensions”. The aforesaid analytical device comprises: a disc-shape holder having a circular groove formed thereon; a magnet set, including a pair of magnets, both disposed on the holder and each magnet in the pair being diametrically opposite to the other magnet in the pair and arranged so that the circular groove is sandwiched between the two magnets. In addition, a rotor magazine, arranged above the holder, is configured with at least a sample cell, each capable of holding and positioning a reaction vessel right on top of the circular groove while being received between the two magnets, by which when the rotor magazine is driven to rotate, the reaction vessels lodged in the sample cells will be driven to move along the circular groove and thus pass the magnetic set at each rotation so that entities of interest can be separate from a mixture containing in the reaction vessel. Nevertheless, an additional driving device is required for driving the rotor magazine to rotate while maintaining the reaction vessel to be positioned and received between the pair of magnets of the magnetic set. As the pair of magnets are diametrically opposite relative to the reaction vessel, and the polar axes of the magnets and the longitudinal axis of the reaction vessel include an acute angle, the holder must be large enough for accommodating the magnetic set as well as for configuring the circular groove thereon that is larger enough for the reaction vessel to pass through.
Another such device is a magnetic capture rack with slidable magnetic member disclosed in U.S. Pat. No. 5,571,481. The aforesaid magnetic capture rack is composed of a housing member having a plurality of sample cells disposed as a linear array, and a slidable and detachable magnetic member. By driving the magnetic member to move in parallel to the linear array of the plural sample cells in a reciprocating manner, magnetic force of the magnetic member can be applied to or removed from the test tubes received in the sample cells according to the reciprocating movement, and thereby, trace entity of interest can be separated from mixtures in the test tubes. It is noted that there must be enough space structured inside the magnetic capture rack for housing the housing member and the magnetic member, and also for enabling the magnetic member to move in such reciprocating manner without being obstructed.
Another such device is a separation device disclosed in EP1621890, entitled “Device and method for separating, mixing and concentrating magnetic particles with a fluid and use thereof in purification methods”, which comprises: a pipette set, including at least a multi-layered pipette arranged as a linear array and each multi-layered pipette being composed of compartments with different cross-section areas; and a magnet set, having at least a magnet arranged as a geometrical array matching the configuration of the pipette set as well as the shape of each multi-layered pipette. As the relative position of the pipette set and the magnet set can be varied by the motions of the magnet set as well as by the raising/descending of the pipette set, entities of interest can be separated from a mixture containing in each pipette in a layer by layer manner. However, such device is difficult to operate as it is not an easy task to maneuver the pipette set and the magnet set into matching positions, not to mention that the device must have enough space for allowing the pipette set to free from the attraction of the magnet set.